# Unsteady Aerodynamics, Dynamic Stall and Dynamic Wake in AeroDyn 15

**URL:** <https://forums.nlr.gov/t/unsteady-aerodynamics-dynamic-stall-and-dynamic-wake-in-aerodyn-15/2198>\
**Category:** Rotor Aerodynamics\
**Created:** [January 27, 2020, 5:46pm UTC](https://forums.nlr.gov/t/unsteady-aerodynamics-dynamic-stall-and-dynamic-wake-in-aerodyn-15/2198 "2020-01-27T17:46:50Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![Jens.Geisler](https://avatars.discourse-cdn.com/v4/letter/j/65b543/32.png) [@Jens.Geisler](https://forums.nlr.gov/u/Jens.Geisler)\
**Post date:** [January 27, 2020, 5:46pm UTC](https://forums.nlr.gov/t/unsteady-aerodynamics-dynamic-stall-and-dynamic-wake-in-aerodyn-15/2198/1 "2020-01-27T17:46:50Z")

</div>

Hi,  
when I get the warning “Turning off Unsteady Aerodynamics because C\_nalpha is 0. BladeNode = 1, Blade = 1”, does that mean that only the dynamic stall feature is disabled for that blade and foil section or also the dynamic inflow/wake effect is turned off?

I am asking, because I’m actually looking for a way to turn off only dynamic stall without turning off dynamic wake. Ideally I would even like to selectively turn off dynamic stall only for some foil sections / nodes, e.g. around the blade tip where the foils have very small chord length which, in combination with the high effective inflow speed, leads to extremely small time constants.

If setting C\_nalpha to zero does in fact turn off dynamic stall and dynamic wake, are there maybe other parameters that I could use to effectively turn off only dynamic stall?

---

<div class="post-metadata">

**Author:** ![Jason.Jonkman](https://dub1.discourse-cdn.com/nrel/user_avatar/forums.nlr.gov/jason.jonkman/32/3086_2.png) [@Jason.Jonkman](https://forums.nlr.gov/u/Jason.Jonkman)\
**Post date:** [January 27, 2020, 7:25pm UTC](https://forums.nlr.gov/t/unsteady-aerodynamics-dynamic-stall-and-dynamic-wake-in-aerodyn-15/2198/2 "2020-01-27T19:25:08Z")

</div>

Dear Jens,

Yes, the warning about “turning off unsteady aerodynamics” only applies to the unsteady airfoil aerodynamics (UA, dynamic stall) model; dynamic wake will still be enabled if it was at initialization.

To disable UA at a given airfoil section, you can set C\_nalpha = 0 or you can set UACutOut = 0.

Best regards,

---

<div class="post-metadata">

**Author:** ![Jens.Geisler](https://avatars.discourse-cdn.com/v4/letter/j/65b543/32.png) [@Jens.Geisler](https://forums.nlr.gov/u/Jens.Geisler)\
**Post date:** [January 28, 2020, 6:58am UTC](https://forums.nlr.gov/t/unsteady-aerodynamics-dynamic-stall-and-dynamic-wake-in-aerodyn-15/2198/3 "2020-01-28T06:58:52Z")

</div>

Great, thanks a lot!